Dynamic quota-based admission control with sub-rating in multimedia servers

An admission control algorithm for a multimedia server is responsible for d etermining if a new request can be accepted without violating the Quality o f Service (QoS) requirements of the existing requests in the system. A nove l quota-based admission control algorithm with sub-rating for two priority classes of requests is proposed in this study. The server capacity is divid ed into three partitions based on the quota values: one for each class of r equests and one common pool shared by two classes of requests. Reward and p enalty are adopted in the proposed system model. High-priority requests are associated with higher values of reward as well as penalty than low-priori ty ones. Given the characteristics of the system workload, the proposed alg orithm finds the best. partitions, optimizing the system performance based on the objective function of the total reward minus the total penalty. The sub-rating mechanism will reduce the QoS requirements of several low-priori ty clients, by cutting out a small fraction of the assigned server capacity , to accept a new high-priority client and to achieve a higher net earning value. A stochastic Petri-Net model is used to find the optimal quota value s and two approximation approaches are developed to find sub-optimal settin gs. The experiment results show that the proposed algorithm performs better than one without sub-rating mechanism, and that the sub-optimal solutions found by the proposed approximation approaches are very close to optimal on es. The approximation approaches enable the algorithm to dynamically adjust the quota values, based on the characteristics of the system workload, to achieve higher system performance.